This invention relates to a cleaning tape for removing unwanted protrusions formed on the surface of a target object for cleaning (or a device substrate) such as a magnetic hard disk, a magnetic head, a semiconductor wafer, a liquid crystal panel or an optical lens, foreign objects such as oily matters attached to the surface of a work piece or stains like oily matters attached to the surface of a target object of cleaning, as well as a method of producing such a cleaning tape. In particular, the invention relates to a burnishing and wiping technology suitable for removing dust attached to the surface of a magnetic disk or a liquid crystal panel or abnormal protrusions formed in a thin-film process.
Devices such as computers, television sets, cameras and telephones are constantly being required to improve their functional properties (such as increased capacity for recording data such as sounds and images and improved smoothness and cleanliness in the case of an image screen (such as a liquid crystal panel) and a camera lens). With such apparatus, it is essential to produce each of the components that comprise the apparatus exactly as designed so as to exhibit the characteristics intended at the design stage.
For example, magnetic hard disks are widely being used as a medium for recording data. Such magnetic hard disks are produced by carrying out a series of surface processing processes such as lapping, polishing and texturing on a non-magnetic substrate such as an aluminum substrate, a glass substrate or a silicon substrate having a Ni—P plating film formed on the surface, and thereafter forming a magnetic recording layer and a diamond-like carbon (DLC) film as a protective film on this magnetic recording layer.
After the protective film is formed in the sequence of the processes described above, its surface is cleaned in order to remove the unwanted protrusions formed on the surface of the protective film and the particles such as dust particles attached to the surface of the protective film.
This cleaning process is generally carried out by using a polishing tape with fixed abrading particles. After this cleaning process, the surface of the protective film is coated with a lubricant of perfluoropolyester type to form a lubricating film, and another cleaning process is carried out for removing attached objects such as dust which have come to become attached to the surface of the lubricating film.
The cleaning process which is carried out for the lubricating film is also carried out by using a polishing tape with fixed abrading particles, as for the cleaning process done for the protective film. These cleaning processes may be carried out each after the Is formation of the protective film or only at the final stage (after the formation of the lubricating film).
As a polishing tape with fixed abrading particles (or a cleaning tape) for removing unwanted protrusions and foreign objects like dust particles attached to the surface, as described above, it has been known (as disclosed, for example, in Japanese Patent Publications Tokkai 8-267364, 9-85628, 10-71572 and 10-114837) to use lapping tapes having hard particles such as alumina (Al2O3) particles, SiC particles and diamond particles fastened to the surface of a base tape made of a synthetic resin such as polyethylene terephthalate and polyamide with a resin material.
Although the relatively hard abrading particles for such polishing tapes with fixed abrading particles (or lapping tapes) which have been in use are capable of removing unwanted protrusions from the surface of a film after the film-forming process, there is a problem in that they cannot sufficiently remove the particles which become attached to the surface of the film after being formed and may even cause scratches on the film surface due to the particles that fall off the polishing layer. In other words, they cannot satisfy the requirement for high degrees of cleanliness and high quality imposed on magnetic hard disks.
In view of this requirement, Japanese Patent Publications Tokkai 8-19965 and 2002-224966 have disclosed cleaning tapes (wiping tapes) using plastic particles for controlling the generation of scratches, and Japanese Patent Publication Tokkai 2001-138249 has disclosed a method of using a foamed sheet for cleaning.
Although these methods are effective in reducing scratches, they are not sufficient for the removal of small protrusions and attached objects, and there remained the problem of poor cleaning effect. It is in particular to be noted that extremely small protrusions (inclusive of foreign objects that are strongly attached to the surface of a substrate) and scratches which have been ignored as being within the range of design error are coming to be not negligible in the production of high-capability devices in the field of high-density recording (and in particular in the field of perpendicular magnetic recording).
Because of the progress in the fabrication technology and thin-film technology for the production of magnetic hard disks, together with the requirement for high levels in cleanliness and quality, the quantity of particles that become strongly attached and Is unwanted protrusions as before is decreasing. On the other hand, however, a new requirement is appearing for cleaning technology for removing even smaller particles and not generating smaller scratches (such as so-called micro-defects).
With a conventional cleaning tape, however, it was not possible to carry out highly efficient clearing or to remove very small particles because the whole of the abrading particles of the cleaning layer does not effectively contact the surface of the target object to be cleaned when it was applied to it (or its abrading particles do not effectively function).